The present invention relates to heat treatment apparatus for the heat treatment of flat objects of processing such as semiconductor wafers, LCD (liquid crystal displays) and the like.
In the manufacture of semiconductor devices for example, processes such as oxidation and diffusion processes, CVD and others are used for semiconductor wafers.
In particular, there has been recent process in degrees of fineness of the design rules for semiconductor devices, and these have changed from 0.4 .mu.m to 0.2 .mu.m. In addition, the semiconductor wafers themselves have been becoming larger, and have changed from 8 inches to 12 inches in diameter and one important problem is the development of technologies for fast heat treatment and which can be used with technologies for the growth of extremely thin films over such a larger area.
More specifically, in semiconductor wafer process processing, one necessary condition is that the thermal budget (or the heat history) be made as small as possible. For example, in the growth of an extremely thin film of a capacitor insulation film or a gate oxidation film by doping processing for 50-100 .ANG. it is essential that the heat treatment be performed quickly, that is, in as short a time as possible.
Not only this, PN junctions for example, have been becoming as thin as 0.1 .mu.m or less, and enabling them to have lower resistances, and the growth of junctions to surfaces of arbitrary shapes requires that the generation of crystal faults be prevented along with the deterioration of the film when the junction is made. However, the active region of PN junctions is narrow and so it is again necessary that the heat treatment be performed as quickly as possible.
In addition, in the growth of a LOCOS oxidation film for example, the synergetic effect of compression stresses in adjacent LOCOS oxidation films is magnified due to the heat cycle and it is easy for changes in the surface potential, leak currents, and reduction of the resist voltage reliability to occur. With respect to these problems, it is necessary to prevent them by reducing the heat cycle by having fast heat treatment of semiconductor wafers.
Also, when there is the use of, for example, of materials having a highly dielectric conductors in the growth of a capacity insulation films, it is necessary to have a system which enables compound process processing by enabling doping and metal film growth to enable the growth of metal oxides (such as Ta.sub.2 O.sub.5 and the like) and polyamides (passivation films).
Thus, the current status of the technology is that semiconductor wafers are becoming larger from 8 inches to 12 inches, and that it is necessary to have fast and uniform heating while reducing the temperature differential between the central and the peripheral portions of the semiconductor wafer, reducing the occurrence of slip, distortion and warping which easily occur in semiconductor wafers, and to prevent them from becoming a hindrance in the manufacture of semiconductor devices.
However, in a conventional type of, vertical batch processing type of heat treatment apparatus, there is a a cylindrical heat source which surrounds the semiconductor wafers which are stacked and housed in a wafer boat of glass, and the semiconductor wafers are heated from the outside towards the center. Because of this, when there is fast heating of the semiconductor wafers, there is a large thermal gradient between the peripheral portions and the center portion of the semiconductor wafers and there is the problem that it is not possible to have uniform heating.